The reclaiming of scrap vulcanized rubber relates to the treating and processing of the vulcanized material to obtain products which are generally plastic and processible in nature and thus suitable for utilization to prepare or produce various articles of manufacture.
Generally, a vulcanized rubber reclaiming process involves the steps of preparation, breakdown and refining.
In the preparation step, scrap vulcanized rubber is divided into small particles, such as by cracking or grinding and most foreign materials such as metal and fiber are removed.
In the breakdown step, the rubber is partially depolymerized and possibly partially devulcanized.
In the refining or finishing process, the reclaimed rubber is recovered from the breakdown station from which it can then be mixed with other reinforcing and processing agents for future use.
In the breakdown step, the vulcanized rubber is typically broken down in the presence of a reclaim oil and peptizer, or catalyst, under conditions of elevated temperature and pressure for a period of time, often also in the presence of water vapor, or steam. Such processes are sometimes called the heater process, the digester process, the Reclaimator process or the high-pressure steam process. Although some vulcanized rubbers can be broken down under a condition of heating alone, peptizers are typically added to speed the degradation process.
Reclaiming peptizers or catalysts may be, for example, aryl sulfides and disulfides.
Reclaiming oils generally function to swell and plasticize the scrap vulcanized rubber in order to make it more receptive to the action of the peptizer.
In the practice of such reclaiming process, a relatively pungent odor of the finished reclaimed rubber has been observed. While not effecting its various physical properties, it has tended to render the finished reclaim rubber objectionable for use in relatively confined areas, particularly where it is used for mixing with other materials, such as other rubbers, the the preparation of other products. It was speculated and considered that some reaction of the disulfide peptizer was with other components in the mixture was occurring to form by-products which created the odorous effect.
However, the inventor discovered, upon fractionating the liquid aryl disulfide, that the mixture in fact contained a dissolved volatile component having a boiling point, at atmospheric pressure, below about 95.degree. C. which was composed primarily of odorous organic mercaptans. The presence of the volatile organic component in the mixture was not earlier observed because, at atmospheric conditions, it remained substantially dissolved in the disulfide and presented little or no obvious odorous effect and thus was not noticeably detected.